This invention relates to a permitted water-bearing explosive composition of either the watergel or emulsion type and to a method of making such a composition.
In general, a permitted or permissible explosive composition is one which has been passed for use by the relevant authorities in fiery mines. The explosive composition must not ignite a mixture of methane and air when the explosive composition is detonated. It has been believed that such permitted explosive composition cannot contain a significant amount of paint flake aluminium because of the high probability that, on detonation, such paint flake aluminium would cause ignition of a methane/air mixture.
In West German Patent No. P2350605.0-45 in the name of IDL Chemicals Limited, there is disclosed a cap sensitive permissible slurry explosive composition which contains an inorganic oxidiser salt, a fuel and a suitable thickening agent. This composition also contains an amount of passivated, finely divided aluminium and a coolant salt. The finely divided aluminium is passivated by treating it with a mono or polyhydroxy alcohol to form a paste, and then adding this passivated aluminium paste to the explosive composition. The coolant salt, which may be common salt, is added in the first step of preparation of the explosive composition when a solution is made of the oxidiser salt or salts.
In South Afican Patent No. 87/2089 in the name of AECI Limited there is disclosed a permitted explosive of the slurry type which comprises a water-soluble inorganic oxidising salt; a water-soluble organic fuel; water; a substance which functions as a heat-absorbing material to reduce the flame temperature of the explosive upon detonation thereof, e.g. calcium nitrate of calcium carbonate; a substance which functions as a flame suppressant, e.g. a metal halide salt such as sodium chloride; and aluminium. The aluminium makes up 1.2 to 1.6% m/m of the explosive, at least 40% m/m of the aluminium being atomized aluminium and any balance of the aluminium being paint fine aluminium.
Atomized aluminium, which differs in shape, size and properties from paint flake (also known as paint fine, paint grade or pigment flake) aluminium, generally has a surface area of up to 1500 cm.sup.2 /g. It is possible to obtain atomized aluminium of 1 micron particle size which may have a surface area of up to 4000 cm.sup.2 /g, but this material is very sensitive and is used only for very specialized applications.
Thus the explosive disclosed in this patent contains no more than 0.96% m/m, (preferably about 0.75% m/m) of the explosive of paint flake aluminium.
The flame suppressant is present in a proportion of 3-4% m/m of the explosive.